Double-ended blower and volutes therefor

ABSTRACT

A variable speed blower for Continuous Positive Airway Pressure (CPAP) ventilation of patients includes two impellers in the gas flow path that cooperatively pressurize gas to desired pressure and flow characteristics. Thus, the blower can provide faster pressure response and desired flow characteristics over a narrower range of motor speeds, resulting in greater reliability and less acoustic noise.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 11/704,325 filedFeb. 9, 2007, pending, which is a continuation of U.S. application Ser.No. 11/135,477 filed May 24, 2005, which is a continuation of U.S.application Ser. No. 10/360,757 filed Dec. 10, 2001, now U.S. Pat. No.6,910,483, each of which are incorporated herein by reference in theirentirety.

FIELD OF THE INVENTION

The present invention relates to an apparatus for supplying breathablegas to a human, used in, for example, Continuous Positive AirwayPressure (CPAP) treatment of Obstructive Sleep Apnea (OSA), otherrespiratory diseases and disorders such as emphysema, or the applicationof assisted ventilation.

DESCRIPTION OF RELATED ART

CPAP treatment of OSA, a form of Noninvasive Positive PressureVentilation (NIPPV), involves the delivery of a pressurized breathablegas, usually air, to a patient's airways using a conduit and mask. Gaspressures employed for CPAP can range from 4 cm H₂O to 28 cm H₂O, atflow rates of up to 180 L/min (measured at the mask), depending onpatient requirements. The pressurized gas acts as a pneumatic splint forthe patient's airway, preventing airway collapse, especially during theinspiratory phase of respiration.

Typically, the pressure at which a patient is ventilated during CPAP isvaried according to the phase of the patient's breathing cycle. Forexample, the ventilation apparatus may be pre-set to deliver twopressures, an inspiratory positive airway pressure (IPAP) during theinspiration phase of the respiratory cycle, and an expiratory positiveairway pressure (EPAP) during the expiration phase of the respiratorycycle. An ideal system for CPAP is able to switch between IPAP and EPAPpressures quickly, efficiently, and quietly, while providing maximumpressure support to the patient during the early part of the inspiratoryphase.

In a traditional CPAP system, the air supply to the patient ispressurized by a blower having a single impeller. The impeller isenclosed in a volute, or housing, in which the entering gas is trappedwhile pressurized by the spinning impeller. The pressurized gasgradually leaves the volute and travels to the patient's mask.

There are currently two common ways in which the blower and impeller canbe configured to produce the two different pressures, IPAP and EPAP,that are required in an ideal CPAP system. A first method is to set themotor/impeller to produce a constant high pressure and then employ adiverter valve arrangement that modulates the high pressure to achievethe required IPAP and EPAP pressures. CPAP systems according to thefirst method are called single-speed bi-level systems with diverters. Asecond method is to accelerate the motor that drives the impeller todirectly produce IPAP and EPAP pressures. CPAP systems according to thesecond method are called variable-speed bi-level systems.

Variable-speed bi-level CPAP systems have a number of particulardisadvantages. A first disadvantage is that in order to switch rapidlybetween IPAP and EPAP, the impeller must be accelerated and deceleratedrapidly. This causes excessive stress on the impeller, motor, andbearings. However, if the impeller is accelerated slowly, the pressurerise may be unsatisfactorily slow, and thus, the patient may not receiveadequate treatment.

Rapid acceleration and deceleration of the motor and impeller alsoresult in excessive heat generation and undesirable acoustic noise.(“Undesirable” acoustic noise, as the term is used here, refers toacoustic noise that is overly loud, as well as acoustic noise whichoccurs at a frequency that is irritating to the user, regardless of itsvolume.) In addition, design engineers are often forced to make acompromise, sacrificing optimal pressure and flow characteristics infavor of achieving a desired peak pressure.

SUMMARY OF THE INVENTION

The present invention, in one aspect, relates to variable speed blowersproviding faster pressure rise time with increased reliability and lessacoustic noise. Blowers according to the present invention comprise agas flow path between a gas inlet and a gas outlet, a motor, and animpeller assembly.

Preferably, the impeller assembly may include a shaft in communicationwith the motor for rotational motion about a first axis and first andsecond impellers coupled, e.g., fixedly secured, to the shaft. Theimpellers are placed in fluid communication with one another by the gasflow path such that both impellers are disposed between the gas inletand the gas outlet to cooperatively pressurize gas flowing from the gasinlet to the gas outlet.

In one embodiment, the impellers are disposed in series between the gasinlet and the gas outlet. The blower may also comprise a housing,portions of the housing being disposed around each of the first andsecond impellers. In particular, the housing may include first andsecond volutes, the first volute containing gas flow around the firstimpeller and the second volute containing gas flow around the secondimpeller. The gas inlet may be located in the first volute and the gasoutlet may be located in the second volute.

The impellers may be arranged such that they are vertically spaced fromone another along the first axis. In particular, they may be disposed atopposite ends, respectively, of the blower housing.

A blower according to the present invention may have varyingconfigurations. In one embodiment, the two impellers are designed torotate in the same direction. In another embodiment, the two impellersare designed to rotate in opposite directions.

Another aspect of the invention relates to an in-plane transitionalscroll volute for use in either a double- or single-ended blower. Thein-plane transitional scroll volute gradually directs pressurized airaway from a spinning impeller.

These and other aspects of the present invention will be described in orapparent from the following detailed description of preferredembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments will be described with reference to thefollowing drawings, in which like reference characters represent likefeatures, wherein:

FIG. 1 is a perspective view of a double-ended blower according to afirst embodiment of the present invention;

FIG. 2 is a partially sectional perspective view of the double-endedblower of FIG. 1;

FIG. 3 is a perspective view of a double-ended blower according to asecond embodiment of the present invention;

FIG. 4 is a sectional perspective view of the double-ended blower ofFIG. 3;

FIG. 5 is a rear perspective view of the double-ended blower of FIG. 3,illustrating the flow therethrough;

FIG. 6 is a perspective view of an in-plane transitional scroll volutesuitable for use in blowers according to the present invention;

FIG. 7 is an exploded perspective view of a double-ended bloweraccording to another embodiment of the present invention;

FIG. 8 is an assembled perspective view of the double-ended blower ofFIG. 7 from one side; and

FIG. 9 is an assembled perspective view of the double-ended blower ofFIG. 7 from another side.

DETAILED DESCRIPTION

Referring now to the Figures, FIG. 1 is a perspective view of adouble-ended blower 100 according to a first embodiment of the presentinvention. Blower 100 has a generally cylindrical shape with impellerhousings, or volutes 112, 113, disposed at each end. Thus, blower 100accommodates two impellers 114, 115, which are best seen in the cut-awayperspective view of FIG. 2.

Referring to FIGS. 1 and 2, the two impellers 114, 115 are placed influid communication with one another by an airpath 116. The airpath 116of blower 100 is comprised of piping that extends from the first volute112 to the second volute 113, the terminal ends of the airpath 116 beingcontoured around, and gradually fusing with, the body of blower 100proximate to the volutes 112, 113 to form a single, integral structure.The airpath 116 may be comprised of rigid piping that is integrallymolded with the other components of the blower 100, or it may becomprised of flexible piping (e.g., metallic or plastic flexiblepiping).

Blower 100 has a single air intake 118 positioned such that air, oranother suitable gas, flows directly into the first volute 112 and canbe drawn in by the turning impeller 114 inside the first volute 112.Once drawn into the air intake 118, the air is circulated andpressurized by the motion of the impeller 114 before gradually exitingthe volute 112 and entering the airpath 116. Once in the airpath 116,the air travels to the second volute 113, where it is further circulatedand pressurized by the impeller 115 of the second volute 113 beforeexiting the blower 100 through the outflow conduit 120. The path of theair in blower 100 is indicated by the arrows in FIG. 1. As shown, inblower 100, air from the first volute 112 travels along a relativelystraight section of the airpath 116 and enters the second volute 113through an intake cavity just above the second volute 113 (not shown inFIG. 1).

Blower 100 could have two air intakes 118, one for each volute 112, 113,if the impellers 114, 115 are designed to work in parallel, rather thanin series. This type of parallel impeller arrangement may be beneficialif installed in a low-pressure CPAP device requiring high flow rates.However, other means for generating high flow rates in a low-pressureCPAP device are known in the art.

The design of the airpath 116 can effect the overall performance of theblower 100. In general, several design considerations influence thedesign of an airpath for use in blowers according to the presentinvention. First, airpaths to be used in blowers according to thepresent invention are most advantageously configured to provide low flowresistance, because low flow resistance in the airpath minimizes thepressure drop between the two volutes 112, 113 in the blower. Second,airpath are best configured such that the air entering the second volute113 enters from a direction for which the blades of the impeller 115were designed. (As will be described in more detail below, the twoimpellers of a blower according to the present invention may be designedto spin in the same or different directions.) Finally, airpaths forblowers according to the present invention are most advantageously of acompact design.

The design considerations set forth above are best embodied in anairpath having long, sweeping bends to minimize the pressure drop aroundthe bends. It is also beneficial to have a relatively straight sectionafter a bend in the airpath, because a relatively straight section aftera bend allows the gas flow to become more fully developed beforeentering a volute. An appropriate length for a straight airpath sectionfollowing a bend is about three times the diameter of the airpath. Therelatively straight section also ensures that the flow entering thesecond volute 113 is axial, the flow orientation for which manyimpellers are designed. If additional flow shaping is desired, statorvanes or other similar flow directing structures may be added to theblower, however, stator vanes may be costly in terms of flow impedanceand pressure drops.

In view of the three major airpath design considerations set forthabove, the airpath 116 of the embodiment depicted in FIG. 1 has a long,relatively straight section because the relatively straight section isone of the shortest possible paths between the two volutes 112, 113.Those skilled in the art will realize that the airpath 116 need not bestraight at all.

Blowers according to the invention may be designed manually, usingprototypes and experimental measurements of air flows and pressures inthose prototypes to optimize the design of the airpath 116 and othercomponents. Alternatively, they may be designed, either as a whole or inpart, by using computational fluid dynamics computer simulationprograms. A variety of computational fluid dynamics programs are knownin the art. Computational fluid dynamics programs particularly suitedfor the design of blowers according to the invention include FLOWORKS(NIKA GmbH, Sottrum, Germany), ANSYS/FLOTRAN (Ansys, Inc., Canonsburg,Pa., USA), and CFX (AEA Technology Engineering Software, Inc., El DoradoHills, Calif., USA). Such simulation programs give the user the abilityto see the effects of airpath design changes on a simulated gas flow.

Many different types of configurations for the two volutes 112, 113 andairpath 116 are possible in a double-ended blower according to thepresent invention. In general, each volute is designed to retain the gasaround the impeller for a short period of time, and to permit a gradualexit of gas into the airpath. The exact configuration of the airpath maydepend on many factors, including the configuration of the volutes andthe “handedness,” or direction of airflow, around each impeller.

The design of the volutes is an art unto itself, as improperly designedvolutes may cause a noise, or may interfere with the generation of thedesired pressure and flow characteristics. The computational fluiddynamics computer programs described above may also be useful indesigning the volutes, although the number of variables involved involute design usually precludes the volute from being entirelycomputer-designed.

One common problem with volutes 112, 113 is that they may provide tooabrupt of a transition into the airpath 116. An abrupt transitionbetween the volute 112, 113 and the airpath 116 usually leaves a forkedpath or “lip” around the opening. When the impeller blades pass by thislip, a noise called “blade passing frequency” is created. Double-endedblowers according to the present invention are particularly suited foruse with volutes that are constructed to reduce the occurrence of “bladepassing frequency” and other noise.

FIG. 6 is a perspective view of an in-plane transitional scroll volute300 suitable for use in a blower according to the present invention.Additionally, the volute 300 may be employed in any conventional blowerapparatus. In the view of FIG. 6, the volute 300 is provided with itsown motor 302, although it may be adapted for use in a double-endedblower having a single motor driving the impellers in two volutes. Asshown, the volute 300 is comprised of two halves 304, 306, the twohalves defining upper and lower portions of the volute 300,respectively. The air intake of the volute 308 is located at the centerof the top half 304. The two halves 304, 306 define a path which slowly“peels” away from the air rotating with the impeller. In the pathdefined by the two halves, there is no sudden “lip” or “split” as inconventional volutes, therefore, “blade passing frequency” is reduced oreliminated entirely. The volute 300 depicted in FIG. 6 is particularlysuitable for relatively short, wide motors.

Alternatively, any common type of volute may be used, depending on thedimensions of the motor installed in the blower. Another suitable typeof volute is the axial volute disclosed in U.S. patent application Ser.No. 09/600,738, filed on Jul. 21, 2000, the contents of which are herebyincorporated by reference herein in their entirety.

One important design consideration for a double-ended blower accordingto the present invention is the “handedness,” or direction of airflow,around each impeller. This “handedness” may be determined by thedirection in which the impeller spins, or it may be determined by theorientation and configuration of the individual blades or vanes of theimpeller. For example, one impeller may be spun or the blades orientedto drive the air in a clockwise direction, and the other impeller may bespun or the blades oriented to drive the air in a counterclockwisedirection, resulting in a “opposing-handed” double-ended blower.Alternatively, both impellers could be driven in the same direction,resulting in a “same-handed” double-ended blower. Blower 100 of FIG. 1is an example of an “opposite-handed” type of double-ended blower.

A “same-handed” blower is advantageous because the two impellers can beidentical, reducing the part count and cost of the blower. However, itshould be noted that a designer may choose to design a “same-handed”blower in which the two impellers are each designed and optimized forthe air flow in their respective volutes.

An “opposing-handed” blower permits the designer to reduce the length ofthe shaft on which the impellers are mounted. This may increase thestability of the shaft itself, because it reduces the problemsassociated with having an imbalance on a long, cantilevered shaftrotating at high speed.

FIG. 3 illustrates a “same-handed” blower 200 according to the presentinvention. Blower 200 also has two volutes 212, 213, an airpath 216, anair intake 218 and an air outlet 220. However, as is shown in FIG. 3,the airpath 216 has the shape of a spiral. That is, airpath 216transitions away from the first volute 212 and then slopes downward asit follows the circumference of the blower 200, before bending andgradually fusing with an intake cavity located between the motor 150 andthe arcuate flange 160, which acts as an air intake in blower 200. Theairflow through the blower 200 is illustrated by the arrows in theperspective view of FIG. 5.

The internal configuration of blower 200 is shown in the partiallysectional perspective view of FIG. 4. The internal arrangements ofblowers 100 and 200 are substantially similar, and will be describedbelow with respect to components of both blowers, Where applicable. Asshown in FIG. 4, an electric motor 150 is installed in the center of theblowers 200. Various types of known brackets and mountings may be usedto support the motor and to secure it to the interior of the blower 200,although for simplicity, these are not shown in FIG. 4.

The motor 150 drives a single shaft 152. The shaft 152 traversessubstantially the entire length of the blower 100, 200 along its center,and is secured to an impeller 114, 115, 214 at each end. The shaft maybe round, square, keyed, or otherwise shaped to transmit power to thetwo impellers 114, 115, 214. The connection between the impellers 114,115, 214 and the shaft 152 may be created by an interference fit betweenthe two parts, a weld, an adhesive, or fasteners, such as set screws. Inblowers 100 and 200, the connection between the shaft 152 and theimpellers 114, 115, 214 is by means of a vertically oriented (i.e.,oriented along the axis of the shaft 152) annular flange 154 formed inthe center of the impellers 114, 115, 214. In FIGS. 3 and 4, theconnection between the impellers 114, 115, 214 and the shaft is shown asan interference fit.

The impeller 114, 115, 214 is substantially annular in shape. The centersection 156 of the impeller 114, 115, 214, is a thin plate which extendsradially outward from the shaft 152 to the blades 158, and is upswept,gradually curving downward as it extends outward from the shaft 152towards the blades 158. The actual diameter of each impeller 114, 115,214 may be smaller than that of a conventional blower with a singleimpeller. Fast pressure rise time in a blower requires a low rotationalinertia, which varies as the diameter to the fourth power. Becauseimpellers 114 and 214 of blowers 100 and 200 are smaller in diameter,they have less rotational inertia, and thus, are able to provide afaster pressure rise time. In addition to diameter, other designparameters of the impellers 114, 214 may be modified to achieve a lowerrotational inertia. Other techniques to reduce rotational inertiainclude “scalloping” the shrouds to produce a “starfish-shaped”impeller, using an internal rotor motor, and using materials, such asliquid crystal polymer, that can be molded into thinner wall sections,so that impeller blades can be hollowed out and strengthened by ribs.

Referring to FIGS. 4 and 5, which show the same-handed, double-endedblower, the top of the first volute 212 is open, forming the air intake118. At the air intake 118, the top surface 120 of the blower 100 curvesarcuately inward, forming a lip 122 over the top of the impeller 214.The upswept shape of the impeller center section 156 and the lip 122 ofthe top surface 120 confine the incoming air to the blower volume insidethe first volute 212 and help to prevent air leakage during operation.An arcuate flange 160 similar to the arcuate top surface 120 extendsfrom the lower interior surface of the blower 200, forming the top ofthe second volute 213. A contoured bottom plate 162, 262 forms thebottom of the second volute 113, 213 of each blower 100, 200. The bottomplate 162 of blower 100 has a hole in its center, allowing the airpath116 to enter, while the bottom plate 262 of blower 200 has no such hole.As described above, the arcuate flange 160 acts as the air intake forthe second volute 213 of blower 200. In blower 200, stator vanes andadditional flow shaping components may be added to the cavity betweenthe motor 150 and the arcuate flange 160 to assist in distributing theincoming air so that it enters the second volute 213 from all sides,rather than preferentially from one side.

As is evident from FIGS. 2 and 4, blowers according to the presentinvention may have many intricate and contoured surfaces. Such contoursare used, as in the case of the arcuate top surface 120 and arcuateflange 160, to direct gas flow and prevent gas leakage. The no-leakrequirement is particularly important when the gas flowing through theblower 100, 200 has a high concentration of oxygen gas. Ifhigh-concentration oxygen is used, gas leakage may pose a safety hazard.Also, apart from any safety considerations, leaking gas may produceunwanted noise, and may reduce blower performance.

The number of intricate, contoured surfaces present in blowers accordingto the present invention makes a production method such as investmentcasting particularly suitable. Although relatively expensive, investmentcasting can produce a single part with many hidden and re-entrantfeatures, whereas other methods of production may require that a designbe split into many parts to achieve equivalent function. However, alarge number of parts is generally undesirable—in order to minimize thepotential for gas leaks, the number of parts is best kept to a minimumand the number of joints between parts is also best kept to a minimum.

There are also a number of materials considerations for blowersaccording to the present invention. Metals are typically used ininvestment casting, but some metals are particularly sensitive tooxidation, which is a concern because medical grade oxygen gas may beused in blowers according to the present invention. One particularlysuitable material for the blowers 100, 200 is aluminum. Whereas steelmay rust on exposure to high concentrations of oxygen, aluminum oxidizesquickly, the oxide forming an impervious seal over the metal. Whichevermetal or other material is used, it is also important that the materialhas a high thermal conductivity and is able to draw heat away from theairpath, to prevent any heat-related ignition of oxygen.

While the use of aluminum has many advantages, it does have a tendencyto “ring,” or resonate, during blower operation. Therefore, dampingmaterials may be installed in an aluminum blower to reduce the intensityof the vibration of the aluminum components.

In blowers 100 and 200, the electric motor 150 is driven at variablespeeds to achieve the desired IPAP and EPAP pressures. The double-ended(i.e., two-stage) design of the blowers means that the range of motorspeeds traversed to achieve the two pressures is reduced. The narrowerrange of motor speeds results in a faster pressure response time thanthat provided by a single-stage blower having similar motor power anddrive characteristics. In addition, the narrower variation in speedapplies less stress to the rotating system components, resulting inincreased reliability with less acoustic noise.

The performance of blowers 100 and 200 is approximately equal to thecombined performance of the two impeller/volute combinations, minus thepressure/flow curve of the airpath 116, 216 between the two volutes 112,113, 212, 213. For a variety of reasons that are well known in the art,the actual performance of the blowers 100, 200 will depend upon theinstantaneous flow rate of the particular blower 100, 200, as well as anumber of factors. At higher flow rates, the pressure drop in theairpath 116, 216 is generally more significant.

Double-ended blowers according to the present invention may be placed ina CPAP apparatus in the same manner as a conventional blower. The bloweris typically mounted on springs, or another shock-absorbing structure,to reduce vibrations.

A Further Embodiment

One further embodiment of the present invention is illustrated in FIG.7, an exploded perspective view of a double-ended blower 400 accordingto the present invention. The motor and stator blade portion 402,located in the center of the exploded view, is investment cast fromaluminum in this embodiment, although other manufacturing methods arepossible and will be described below. The aluminum, as a good conductorof heat, facilitates the dissipation of heat generated by theaccelerating and decelerating motor. Each end of the shaft 404 is shownin FIG. 7, but the motor windings, bearing and cover are not shown. Themotor power cord 406 protrudes from the motor and stator blade portion402 and exits the blower 400 through a sealed orifice 450. The motor andstator blade portion 402 includes, at its top, a bottom portion of theupper volute 408.

As a variation of the design illustrated in FIG. 7, the motor and statorblade portion 402 may be made separately from the bottom portion of theupper volute 408. If the two components are made separately, investmentcasting would not be required. For example, the motor body may be diecast, while the bottom portion of the upper volute 408 may be injectionmolded.

Secured to the motor and stator blade portion 402 by bolts or otherfasteners is a circular plate 410, in which a hole 412 is provided forthe passage of the shaft 404. An impeller 414 rests atop the circularplate. The impeller 414 is scalloped along its circumference to reduceits rotational inertia, giving it a “starfish” look.

An upper endcap 416 is secured above the impeller 414, and provides thetop portion of the upper volute. The upper and lower volutes in thisembodiment are versions of the in-plane transitional scroll volute 300illustrated in FIG. 6. An aperture 418 in the center of the upper endcap416 serves as the air intake of the blower 400.

On the lower end of the blower 400, a contoured plate 420 forms the topportion of the lower volute. The top of the contoured plate 420 israised and curves arcuately downward toward a hole 422. As was explainedabove, the contoured plate 420 helps to shape the airflow and to ensurethat it enters the impeller cavity from all sides, rather thanpreferentially from a single direction. Beneath the contoured plate 420,a lower impeller 414 rotates proximate to a lower endcap 428. The twoendcaps, 416, 428 may be die cast (e.g., from aluminum or magnesiumalloy) or they may be injection molded from an appropriate metal.

The airpath 454 between the upper and lower volutes is an integral partof the left 424 and right 426 side casings, onto which the othercomponents are secured. The left side casing 424 also provides the airoutlet 442 for the blower 400. The left 424 and right 426 side casingsare secured together with bolts or other removable fasteners. On the topsurface of the side casings 424, 426 are square flanges 430, 432 havingprotrusions 434, 436 that allow the blower 400 to be mounted on springsinside a CPAP apparatus. In FIG. 7, the protrusions 434, 436 are shownas having different sizes and shapes, however, in FIGS. 8 and 9, theprotrusions 434 are shown as having the same shape. It will be realizedthat the protrusions 434, 436 may take either of the depicted shapes, orany other shape, depending on the properties and arrangement of thesprings onto which the blower 400 is mounted.

The double-ended blower 400 also includes two damping sleeves 438, 440.The damping sleeves 438, 440 are rubber or foam rubber components thatare injection molded to match the internal contours of the left 424 andright 426 side casings, respectively. In one implementation, the dampingsleeves 438, 440 are 40 Shore A hardness polyurethane formed from arapid prototype silicone mold. Alternatively, the damping sleeves 438,440 could be silicone, or another elastomer that is stable at the hightemperatures generated by the motor.

The damping sleeves 438, 440 serve three major purposes in blower 400:they form the actual airpath 454, they provide a seal between the othercomponents, and they dampen the vibrations of the other parts. Therubber or foam rubber material of the damping sleeves 438, 440 isparticularly suitable for the airpath 454, as it allows for re-entrantmolds (i.e., undercuts). The damping properties of the damping sleeves438, 440 reduce the “ringing” of the aluminum components that wouldotherwise be experienced.

FIG. 8 is an assembled perspective view of blower 400 from one side. Theassembled air outlet 442 is shown in FIG. 8, as is the seam 444 betweenthe left 424 and right 426 side casings. As shown in FIG. 8, and in therotated perspective view of FIG. 9, flanges 446, 448 protrude laterallyfrom the edge of each side casing 424, 426 and abut to form the seam444. The two side casings 424, 426 are secured together by bolts 452that pass through the flange 446 provided in the right side casing 426and into threaded holes provided in the flange 448 of the left sidecasing 424.

Blower 400 has several advantages. First, investment casting is notrequired to produce blower 400, which reduces the cost of the blower.Additionally, because the components of blower 400 have fewer hidden andintricate parts, the castings can be inspected and cleaned easily.Finally, blower 400 is easier to assemble than the other embodimentsbecause the components are clamped together using the two side casings424, 426, which can be done with simple fasteners.

While the invention has been described by way of example embodiments, itis understood that the words which have been used herein are words ofdescription, rather than words of limitation. Changes may be madewithout departing from the scope and spirit of the invention in itsbroader aspects. Although the invention has been described herein withreference to particular embodiments, it is understood that the inventionis not limited to the particulars disclosed. The invention extends toall appropriate equivalent structures, uses and mechanisms.

The invention claimed is:
 1. A CPAP/NIPPV apparatus for treatment of apatient with a sleeping disorder, the apparatus including a blower forsupplying breathable gas to the patient, comprising: a casing; a gasflow path between a gas inlet and a gas outlet of said casing; a motorlocated within said casing; a motor drive shaft including a first shaftend and a second shaft end defining a rotational axis, said first andsecond shaft ends extending from opposite sides of the motor; a firstimpeller within a first volute and secured to the first shaft end, saidfirst impeller including a first gas intake, said gas inlet axiallyaligned along said rotational axis with the first impeller; and a secondimpeller within a second volute and secured to the second shaft end,said second impeller including a second gas intake, said first andsecond impellers being disposed axially between said gas inlet and saidgas outlet to cooperatively pressurize gas flowing from said gas inletto said gas outlet, wherein said first and second gas intakes arecoaxial with said motor drive shaft, and wherein the gas flow pathincludes a length of piping outside said casing connecting said firstand second volutes.
 2. A CPAP/NIPPV apparatus as claimed in claim 1,wherein said length of piping is comprised of substantially rigidpiping.
 3. A CPAP/NIPPV apparatus as claimed in claim 1, wherein saidlength of piping is comprised of flexible piping.
 4. A CPAP/NIPPVapparatus as claimed in claim 1, wherein said length of piping includesbends adjacent said first and second volutes with a straight sectionbetween said bends.
 5. A CPAP/NIPPV apparatus as claimed in claim 1,wherein said length of piping has a diameter, and wherein said straightsection has a length of about three times said diameter.
 6. A CPAP/NIPPVapparatus as claimed in claim 1, wherein said length of piping has aspiral shape.
 7. A CPAP/NIPPV apparatus as claimed in claim 1, whereinsaid second intake is defined by an annular, arcuate flange surroundingsaid second shaft end.
 8. A CPAP/NIPPV apparatus as claimed in claim 1,wherein said first and second impellers are configured for rotation inthe same direction.
 9. A CPAP/NIPPV apparatus as claimed in claim 1,wherein said first and second impellers comprise blades configured todirect the gas in a common direction.
 10. A CPAP/NIPPV apparatus asclaimed in claim 1, wherein said first and second impellers areconfigured for rotation in opposite directions.
 11. A CPAP/NIPPVapparatus as claimed in claim 1, wherein said motor is driven to achievedesired IPAP (inspiratory positive airway pressure) and EPAP (expiratorypositive airway pressure) pressures.
 12. A CPAP/NIPPV apparatus asclaimed in claim 1, further comprising a patient interface including amask.
 13. A CPAP/NIPPV apparatus as claimed in claim 1, wherein theCPAP/NIPPV apparatus is pre-set to deliver inspiratory positive airwaypressure (IPAP) during an inspiratory phase of the patient's breathingcycle, and to deliver expiratory positive airway pressure (EPAP) duringan expiration phase of the patient's respiratory cycle.
 14. A CPAP/NIPPVapparatus as claimed in claim 13, wherein the IPAP is greater than theEPAP.
 15. A CPAP/NIPPV apparatus as claimed in claim 1, wherein theblower is configured to generate pressures in the range of about 4 cmH₂O to 28 cm H₂O at flow rates of up to of about 180 L/min as measuredat a patient interface.
 16. A CPAP/NIPPV apparatus as claimed in claim1, wherein said first and second impellers are arranged in series toserially pressurize gas flowing from said gas inlet to said gas outlet.17. A CPAP/NIPPV apparatus as claimed in claim 1, wherein said motor isa variable speed motor.
 18. A CPAP/NIPPV apparatus as claimed in claim1, further comprising a patient interface including a mask.
 19. ACPAP/NIPPV apparatus as claimed in claim 1, wherein said second gasintake is located axially between said motor and said second volute. 20.A CPAP/NIPPV apparatus as claimed in claim 19, wherein said second gasintake is located axially between said motor and said second volute.